Among perennials, super summer performers with long bloom periods include Astilbe, daylilies (Hemerocallis), purple coneflower (Echinacea purpurea), Gaillardia, garden phlox, Monarda, Rudbeckia, and Perovskia. Verbena bonariensis is one of my favorite summer flowers. Some early blooming perennials will rebloom later in the season if cut back after the early bloom flush. Among these are yarrow (Achillea), Tradescantia, many cranesbills (perennial geraniums), veronicas and salvias.